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Re: Pg_upgrade speed for many tables

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Magnus Hagander <magnus(at)hagander(dot)net>,PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Pg_upgrade speed for many tables
Date: 2012-11-05 20:49:08
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Lists: pgsql-hackers
On Mon, Nov  5, 2012 at 03:30:32PM -0500, Tom Lane wrote:
> Magnus Hagander <magnus(at)hagander(dot)net> writes:
> > On Mon, Nov 5, 2012 at 9:14 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> BTW, does pg_upgrade run pg_restore in --single-transaction mode?
> >> That would probably make synchronous_commit moot, at least for that
> >> step.
> > It doesn't use pg_restore at all - it uses the dump from pg_dumpall, which
> > you can't reload with pg_restore.
> Sorry, I should've said psql --single-transaction.  Although that isn't
> going to work either given the presence of \connect commands in the
> script.  I wonder whether pg_dumpall ought to have some sort of "one
> transaction per database please" option.

pg_dumpall is already doing lots of gymnastics with SQL, and pg_upgrade
splits the output file into db/user creation and object creation, so I
am hesitant to add anything more in there.

I was surprised by the scale of the performance improvement, but a
simple table creation test confirmed that improvement, irregardless of
pg_upgrade.  Perhaps we should suggest synchronous_commit=off for
pg_dumpall restores, particularly when using --schema-only.

  Bruce Momjian  <bruce(at)momjian(dot)us>

  + It's impossible for everything to be true. +

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